[Drug allergy].

Drug allergies represent about 10% of all adverse drug reactions. According to the Gell and Coombs classification, they are based on immunological mechanisms, with sensitization during the first contact, and later a clinical and (or) biological reaction after the second contact. Metabolism of drugs, often genetically determined, results in reactive metabolites which conjugate with endogenous proteins to become immunogenic. Anaphylaxis induced by myorelaxant drugs and beta-lactams, and delayed type drug eruptions are discussed as examples. All acute drug reactions are not, however, anaphylactic. Many exanthematous reactions occurring during antibiotic treatment are in fact caused by a virus.